25 



will be produced so long as the seeds arc large enough to pro- 

 duce vigorous plants. 



The farmer and the plant-breeder may plant the small potato 

 tubers or the small seeds without any danger of detenoration in 

 the yield and quality of the crop provided they select these 

 tubers or seeds from plants which yield the largest quantity and 

 the finest quality of tubers or of seeds. 

 Station for E.kperimkntal Evolution, 

 Cold Spring Harbor, Long Island. 



SOIL WATER IN RELATION TO TRANSPIRATION 



By V. M. Spalding 



In a recent article by the writer on the creosote bush in its 

 relation to water supply,* the statement was made that the 

 amount transpired appears to stand in direct relation to the 

 amount of water available in the soil in which the plant is grow- 

 ing. Further observations on this and some other desert plants 

 not only confirm this view but go to show that water in the soil 

 is a controlling factor, and that even as efficient an agent as light 

 may, in comparison, take quite secondary rank. 



The later literature of transpiration, however voluminous in 

 general, is extremely limited as regards this branch of the sub- 

 ject. t Aloi and Ferruzza have shown that the amount of water 

 in the soil is a factor by which the opening of stomata, and con- 

 sequently the rate of transpiration, is controlled, and Stenstrom 

 has attempted to formulate a mathematical equivalency between 

 the rate of transpiration and the ratio of atmospheric and soil 

 moisture. The remaining literature dates from the works of 

 Sachs and older writers. 



In the summer of 1904, while engaged in observing the influ- 

 ence of light of different degrees of intensity on transpiration, I 

 found that results apparently conflicting became consistent when 

 account was taken of the amount of water supplied to the plants 

 under investigation and the time at which it was given. 



* Botanical Gazette, 38: 122. 1904. 



•f- lUirgeisteiii, A. Die 'rranspiration der Ptlanzen. 137. 1904. 



